Hi Folks,
I've built a version of the IR LED driver circuit from here: http://www.robotroom.com/Infrared555.html and I'm having some trouble getting it to work.
The timer is putting out a 38kHz signal, at 4.38v. (The duty cycle is wrong -- closer to 65% than 50% -- but that's a different question.)
The problem is that when I connect the transistor, even with no load on it, the signal out of the 555 drops to about a .6 volt square wave, and the signal out of the transistor is about -5v relative to my positive bus, with about a .4v square wave on top of that -- in other words, the transistor is mostly on all the time, only varying the output voltage by about 0.4v.
It seems vaguely similar to the issue mentioned in this post, though the application is fairly different: http://forum.allaboutcircuits.com/showthread.php?t=29992
The transistor is a 2N2222 NPN, as specified in the design. The only difference between my components and the specifications is that I didn't have a 4.7k resistor on hand, so I've used a 5.6k between the 555 output and the base on the transistor instead. I also tried with a 3.3k though, and it didn't change the results I'm getting, so I don't think that's the problem.
As anyone reading this has probably guessed, I don't know much about transistors! If anyone has an idea what I could be doing wrong, it would be great to hear about it.
Thanks for your help,
Adam
I've built a version of the IR LED driver circuit from here: http://www.robotroom.com/Infrared555.html and I'm having some trouble getting it to work.
The timer is putting out a 38kHz signal, at 4.38v. (The duty cycle is wrong -- closer to 65% than 50% -- but that's a different question.)
The problem is that when I connect the transistor, even with no load on it, the signal out of the 555 drops to about a .6 volt square wave, and the signal out of the transistor is about -5v relative to my positive bus, with about a .4v square wave on top of that -- in other words, the transistor is mostly on all the time, only varying the output voltage by about 0.4v.
It seems vaguely similar to the issue mentioned in this post, though the application is fairly different: http://forum.allaboutcircuits.com/showthread.php?t=29992
The transistor is a 2N2222 NPN, as specified in the design. The only difference between my components and the specifications is that I didn't have a 4.7k resistor on hand, so I've used a 5.6k between the 555 output and the base on the transistor instead. I also tried with a 3.3k though, and it didn't change the results I'm getting, so I don't think that's the problem.
As anyone reading this has probably guessed, I don't know much about transistors! If anyone has an idea what I could be doing wrong, it would be great to hear about it.
Thanks for your help,
Adam
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